Computer disk drives store information on magnetic disks. Typically, the information is stored on each disk in concentric tracks, divided into sectors. Information is written to and read from a disk by a head (or transducer), which is mounted on an actuator arm capable of moving the head radially over the disk. Accordingly, the movement of the actuator arm allows the head to access different tracks. The disk is rotated by a spindle motor at a high speed, allowing the head to access different sectors on the disk. The head may include separate or integrated read and write elements.
A disk drive 10 is illustrated in FIG. 1. The disk drive comprises a disk 12 that is rotated by a spin motor 14. The spin motor 14 is mounted to a base plate 16. The disk drive 10 also includes an actuator arm assembly 18 having a head 20 (or transducer) mounted to a flexure arm 22, which is attached to an actuator arm 24 that can rotate about a bearing assembly 26 that is attached to the base plate 16. The actuator arm 24 cooperates with a voice coil motor 28 in order to move the head 20 relative to the disk 12. The spin motor 14, voice coil motor 28 and head 20 are coupled to a number of electronic circuits 30 mounted to a printed circuit board 32. The electronic circuits 30 typically include a read channel chip, a microprocessor-based controller and a random access memory (RAM) device. Instead of a one disk configuration (shown in FIG. 1), the disk drive 10 may include a plurality of disks 12 and, therefore, a plurality of corresponding actuator arm assemblies 18.
FIG. 2 is a diagrammatic representation of a simplified top view of a disk 12 having a surface 42 which has been formatted to be used in conjunction with a sectored servo system (also known as an embedded servo system). As illustrated in FIG. 2, the disk 12 includes a plurality of concentric tracks 44a-44h for storing data on the disk's surface 42. Although FIG. 2 only shows a relatively small number of tracks (i.e., 8) for ease of illustration, it should be appreciated that typically tens of thousands of tracks are included on the surface 42 of a disk 12.
Each track 44a-44h is divided into a plurality of data sectors 46 and a plurality of servo sectors 48. The servo sectors 48 in each track are radially aligned with servo sectors 48 in the other tracks, thereby forming servo wedges 50 which extend radially across the disk 12 (e.g., from the disk's inner diameter 52 to its outer diameter 54).
One of the operations that a disk drive performs is known as a seek operation. During a seek operation, the head 20 is moved from a present track of the disk to a target track of the disk, so that a data transfer can be performed with the target track. In order for a seek operation to be performed, a current is delivered to the VCM 28 of the disk drive, which causes the actuator arm 24 to rotate, thereby moving the head 20 radially relative to the disk surface 42.
It is desirable to perform seek operations as quickly as possible. Accordingly, in conventional long seek operations, for example, a maximum current will be applied to the VCM 28 in a first direction for a period of time to accelerate the head 20 towards a maximum velocity as it moves towards the desired track. Once the head 20 reaches its maximum velocity, no current is applied to the VCM 28 and the head 20 coasts at its maximum velocity for a period of time. Just prior to reaching the target track, in order to decelerate the head 20, a maximum current is applied to the VCM 28 in a direction opposite to the first direction, such that the head 20 is positioned near the target track. Once near the target track, the drive 10 may enter a linear mode to position the head 20 more closely to the target track. A diagrammatic representation of such a bang-coast-bang current profile is illustrated in FIG. 3.
Application of currents in such a fashion causes abrupt changes in the acceleration and deceleration of the head. This tends to excite vibration modes in the drive, which can cause acoustic noise due to seek operations (also known as seek acoustics). If seek acoustics are not kept within acceptable levels, a disk drive may fail to meet qualification standards, which reduces drive yields and increases the overall manufacturing costs of disk drives.
Accordingly, it would be advantageous to provide a method and apparatus for reducing seek acoustics in a disk drive system. At the same time, however, it would be desirable to provide such a method and apparatus, which does not significantly compromise seek performance.